Metal casting mold for centrifugal casting machine

ABSTRACT

A metal casting mold of double wall construction to be used for a centrifugal casting machine is made of an inner casting mold member and an outer mold member concentrically fixed thereto with plastically deformable spacing members. The inner mold member is fixed in the outer mold member and interposed between a pair of end covers having on the inner side face thereof a sand mold for absorbing the expansion of the inner mold member in the axial direction. The radial thermal expansion of the inner mold member is absorbed by the spacing member. The end covers are tightly fixed to both ends of the inner mold member by means of pins.

Sekimoto et a1.

METAL CASTING MOLD FOR CENTRIFUGAL CASTING MACHINE Inventors: Yasuhiro Sekimoto; Yoshitada Miura, both of Kitakyushu, Japan Assignee: Hitachi Metals, Ltd., Japan Filed: Aug. 9, 1972 Appl. No.: 279,654

Foreign Application Priority Data Aug. 11, 1971 Japan 46-60321 US. Cl. 164/286; 164/114 Int. Cl. 822d 13/00 Field of Search 164/286, 289, 303, 175, 164/287, 300, 302, 33, 43, 114, 298, 361, 290-295 2/1938 Anderson... 164/293 3/1938 Marvin 164/290 [451 Aug. 12, 1975 2,123,037 7/1938 Carrington 164/29] 2,489,322 ll/l949 Olsen 164/286 2.727,288 12/1955 Saives 164/293 Primary Examiner-Francis S. l-lusar Assistant Examiner-John S. Brown Attorney, Agent, or Firm-Craig & Antonelli [57] ABSTRACT A metal casting mold of double wall construction to be used for a centrifugal casting machine is made of an inner casting mold member and an outer mold member concentrically fixed thereto with plastically deformable spacing members. The inner mold member is fixed in the outer mold member and interposed between a pair of end covers having on the inner side face thereof a sand mold for absorbing the expansion of the inner mold member in the axial direction. The radial thermal expansion of the inner mold member is absorbed by the spacing member. The end covers are tightly fixed to both ends of the inner mold member by means of pins.

5 Claims, 3 Drawing Figures PATENTED M151 2 I975 PRIOR ART FIG. 2

' FIG. 3

METAL CASTING MOLD FOR CENTRIFUGAL CASTING MACHINE This invention relates to a metal mold, and more particularly to a metal mold for use in a centrifugal casting machine. 1

Centrifugal casting is a method of casting wherein molten metal is introduced into a rotating mold and solidified therein. The products made by the centrifugal casting have been limited heretofore to solid columnar articles having small diameter and hollow cylindrical articles having a comparatively thin wall. Since the thermal capacity of the products issmaller than that of the metal mold in these cases, the temperature of the metal mold does not rise as high as that of the products. Therefore, a metal mold of solid construction'has been used without any problems. However, when casting large size solid columnar articles or large size of sleeve having a thick wall by the centrifugal casting method, it takes a long time for the molten metal to be solidified due to its large thermal capacity and there is a fear of breaking the mold and/or causing vibration thereof because of thermal distortion of the metal mold caused by the temperature rise thereof of the solid type and the increased thermal stress generated therein. In a centrifugal casting machine in which a mold is rotated at a high speed, these problems have a great influence both on the quality of the products and on the safety of operation thereof.

The object of the present invention is to provide a metal mold for centrifugal casting in which there is generated only a small thermal stress.

Another object of the present invention is to provide a metal mold for centrifugal casting which is not subject to vibration when the centrifugal casting machine is operated.

Still another object of the present invention is to provide a metal mold for centrifugal casting in which the size of the articles molded thereby can be easily changed.

In order to accomplish the above objects, the meta mold in accordance with the present invention comprises an outer mold member and an inner mold member concentrically coupled with each other defining a cylindrical space therebetween whereby the temperature gradient within the metal mold members is reduced by the heat insulating effect of the space. Further, plastically deformable spacing members are inserted between the outer and inner mold members to fix the inner and outer metal mold members together whereby reducing the vibration of the metal mold as well as absorbing thermal expansion of the inner mold member. Besides, since the metal mold is formed in a double wall construction in the present invention, the size of the article can be easily changed by changing the size of the inner mold member and the number of the metal molds to be prepared can be reduced.

Other objects, features and advantages of the present invention will be made apparent from the following detailed description of the preferred embodiment thereof taken in conjunction with the accompanying drawing wherein;

FIG. 1 is a longitudinal sectional view of a prior art metal mold for centrifugal casting,

FIG. 2 is a longitudinal sectional view of the metal mold for centrifugal casting in accordance with an embodiment of the present invention, and

FIG. 3 is an enlarged partial sectional view of the metal mold as shown in FIG. 2.

Referring first to FIG. 1 showing an example of the prior art metal mold used for centrifugal casting, of the solid type of construction, a' metal mold 1 coated on the intemal surface thereof with a coating layer is usually provided at the opposite ends thereof with a pair of end covers 3 carrying a sand mold 2 fixed thereto by means of pins 4 so that the molten metal poured thereinto may not be scattered. The internal temperature of the metal mold unit after the molten metal is poured therein normally rises over 400C, and differs according to the kind of coated material and the thickness thereof. The wall thickness of the metal mold is usually increased in proportion to the thermal capacity of the articles to be molded. Since the temperature gradient formed radially in the metal mold becomes larger in this case, the tensile thermal stress generated on the outer surface of the metal mold becomes larger and the load on the pins 4 by the axial thermal expansion on the internal surface of the metal mold increases as well as the thermal distortion of the whole metal mold. In the case of the metal mold which is rotated at a high speed, the centrifugal forces of the molten metal and the metal mold itself act on the mold unit and accordingly it is necessary to carefully select the strength of the metal mold in comparison with the stationary type metal mold.

Referring now to FIGS. 2 and 3 showing an embodiment of the present invention, the metal mold comprises an outer mold member 8 and an inner mold member 5. The inner metal mold member 5 has a flange construction 6 at one end (right hand side) thereof and is provided on the outer periphery thereof with a plurality of plastically deformable spacing members 7 such as of copper alloy having a predetermined height and size and being spaced apart equally around the inner metal mold member 5 at predetermined positions. The inner mold member 5 provided with the spacing member 7 therearound is inserted into an outer mold member 8. A pair of end covers 10 each having a sand mold 9 at its inside face are located at opposite ends of the inner metal mold member 5 and fixed there by means of pins 11. The end covers 10 are only in contact with the outer mold'member 8 and are not in contact with the inner mold member 5. Instead, the sand molds 9 attached to the end covers I0 does contact with the inner mold member.

In operation, when the above described double wall construction type of metal mold is used for the centrifugal casting, the whole inner metal mold member 5 is quickly heated and there arises no serious high temperature gradient within the inner mold member 5 since the thickness of the inner metal mold member 5 is comparatively thin and is thermally shielded from the outer metal mold member 8 when the inner mold member 5 is first heated by the molten metal. When the temperature of the whole inner metal mold member 5 rises, the mold member 5 naturally, expands thermally. The thermal expansion thereof, however, is not transmitted directly to the outer metal mold member 8 because the spacing members 7 are compressed and thermally distorted between the inner and outer mold members, but they can be serviceable for repeated use. Further, since the axial expansion of the inner metal mold member 5 is absorbed by one of the sand molds 9 at the free (right hand side of FIG. 2) end portion thereof, the force loaded on the pins 11 is considerably weakened. Al-

though the temperature of the outer metal mold member 8 rises as the spacing members 7 transmit heat thereto from the inner metal mold member 5 when the spacing members 7 are compressed therebetween by the thermal expansion of the inner metal mold member 5, the temperature gradient of the outer metal mold member 8 is small and the thermal stress generated within the outer metal mold member 8 is small since heat is not directly transmitted thereto from the molten metal. Since the thermal expansion of the inner metal mold member 5 is restricted to some extents by the outer metal mold member 8 after the inner metal mold member 5 comes closer to the outer metal mold member 8, a tensile stress generates, which results in breakage of the outer metal mold member 8 in addition to the thermal stress. Therefore, the dimension of the space between the inner and outer metal mold members 5 and 8 should be determined so that the total stress may be smaller than that of the prior art type solid metal mold. The dimensions of the space can be determined by actual measurement and theoretical calculation as shown in the following table:

diameter of inner member When the double wall type casting mold in accordance with the present invention was used to cast large size casting products, there was little vibration of the mold during the casting operation and there was little thermal distortion left after the operation as expected. When a number of large size sleeves having wall thickness of not less than 100 mm and diameter of not less than 800 mm were manufactured by use of the casting mold in accordance with the present invention, the quality of the products was excellent and no fractures were found in the mold even after being used more than 50 times. Thus, it was also proved that the present invention has a remarkable effect in the sense of safety in large sized centrifugal casting machines.

We claim:

1. A metal mold assembly of double wall construction adapted to be used for centrifugal casting comprising:

an inner metal mold member,

an outer metal mold member concentrically provided around said inner metal mold member, said outer and inner metal mold members being concentrically spaced from one another at a dimension for minimizing the total tensile and thermal stresses in said inner and outer metal mold members, wherein said dimension is not less than about 0.13 percent of the outer diameter of said inner metal mold member, and said outer and inner metal mold members being mounted with respect to each other for rotation about an axis concentric to said outer and inner members,

a plurality of plastically deformable spacing members spaced apart from each other and inserted between said inner metal mold member and said outer metal mold member for reducing vibration of said metal mold during casting operations and simultaneously for permitting radial thermal expansion of said inner metal mold member free of distortion, and

a pair of end covers provided in contact only at opposite axial ends of said outer metal mold member, each of said end covers having on the inner face thereof a sand mold in direct contact with the opposing axial end of said inner metal mold member, said inner metal mold member being entirely prevented at one axial end from direct contact with said end covers so that axial expansion of said inner metal mold member is absorbed only by said sand mold.

2. A metal mold of double wall construction adapted to be used for centrifugal casting as defined in claim 1 wherein said end covers are fixed in the outer metal mold member by means of pins.

3. A metal mold assembly according to claim 1, wherein said dimension is from about 1.4 mm to about 2 mm, said inner metal mold member having an outer diameter of from about 1048.6 mm to about 1570 mm and said outer metal mold member-having an inner diameter of from about 1050 mm to about 1580 mm.

4. A metal mold assembly according to claim 1, wherein said plurality of plastically deformable spacing members are arranged equally around said inner metal mold member at predetermined positions.

5. A metal mold assembly according to claim 1, wherein said plurality of plastically deformable spacing members are of a copper alloy. 

1. A metal mold assembly of double wall construction adapted to be used for centrifugal casting comprising: an inner metal mold member, an outer metal mold member concentrically provided around said inner metal mold member, said outer and inner metal mold members being concentrically spaced from one another at a dimension for minimizing the total tensile and thermal stresses in said inner and outer metal mold members, wherein said dimension is not less than about 0.13 percent of the outer diameter of said inner metal mold member, and said outer and inner metal mold members being mounted with respect to each other for rotation about an axis concentric to said outer and inner members, a plurality of plastically deformable spacing members spaced apart from each other and inserted between said inner metal mold member and said outer metal mold member for reducing vibration of said metal mold during casting operations and simultaneously for permitting radial thermal expansion of said inner metal mold member free of distortion, and a pair of end covers provided in contact only at opposite axial ends of said outer metal mold member, each of said end covers having on the inner face thereof a sand mold in direct contact with the opposing axial end of said inner metal mold member, said inner metal mold member being entirely prevented at one axial end from direct contact with saiD end covers so that axial expansion of said inner metal mold member is absorbed only by said sand mold.
 2. A metal mold of double wall construction adapted to be used for centrifugal casting as defined in claim 1 wherein said end covers are fixed in the outer metal mold member by means of pins.
 3. A metal mold assembly according to claim 1, wherein said dimension is from about 1.4 mm to about 2 mm, said inner metal mold member having an outer diameter of from about 1048.6 mm to about 1570 mm and said outer metal mold member having an inner diameter of from about 1050 mm to about 1580 mm.
 4. A metal mold assembly according to claim 1, wherein said plurality of plastically deformable spacing members are arranged equally around said inner metal mold member at predetermined positions.
 5. A metal mold assembly according to claim 1, wherein said plurality of plastically deformable spacing members are of a copper alloy. 